White man gets sent to spy on the savage enemies. He earns their trust and falls in love with the chief's daughter. White man's army attacks the savages. The savages, and the chief's daughter feel betrayed, and want nothing to do with the white man. The white man gets torn between both civilizations, and redeems himself by being the savages' hero in the fight against the white man army. At the ending, he is seen joining the savages, as the white man army flees the planet.
That's the plot of the movie. Now the characterization.
Protagonist, Jake Skully is meant to be an every-man that the viewers are supposed to identify with, but Sam Worthington does not succeed. He comes off like an obnoxious idiot, with more guts than brains, as demonstrated by his consistently annoying one-liners, sociological ignorance, and overall demeanor. Yet, somehow, he is able to do what all the humans have failed miserably to do for the longest time: win the trust of the Na'vi.
And thus, all this, and especially the special effects has made Avatar into the most successful movie of all time. This led to a massive three day discount sale for the DVD and Blu-ray, that knocked a few dollars off the price tag, if bought within these first three days. The DVD itself can be bought for cheaper than the DVD/Blu-ray combo, but that is little reason for anybody to purchase the more expensive version, if they do not already own a Blu-ray player. It is quite obvious, that in the near future, James Cameron is going to release a special two disc director's cut edition of the movie, that's going to contain extras, as the current DVD only has the movie, and nothing else.